Plasticizers, as polymer additives, have been known for more than a century. Most high volume plasticizers have been developed in the last seventy years, primarily for use with vinyl and other polymeric substances. Plasticizers are used more than any other type of polymer additives, particularly in polyvinyl chloride (PVC) applications. Hundreds of plasticizers have been produced, but only a few remain having acceptable performance properties when combined with vinyl or other polymeric materials.
General purpose phthalates dominate the volume of plasticizers purchased every year and are most often selected for compounding flexible vinyl.
A typical plasticizer is defined as an organic liquid that will soften a polymer and make it more workable, as long as the polymer and plasticizer are at least partially compatible. The function of a plasticizer in any polymer system requires compatibility. Plasticizers are used to adjust hardness (or softness) of a polymer, impart stain resistance, alter tensile properties (such as strength, elongation or flexibility) and to facilitate processability, as required, for a multitude of applications, including without limitation flexible vinyl applications.
Plasticizers also serve as a vehicle for the dispersion of resin (polymer) particles, such as PVC. The dispersion is initially a two-phase, heterogeneous system. Plasticizers promote the formation of homogeneous systems and polymer fusion occurs upon heating. The higher the solvating power, the lower the temperature at which a homogeneous system is fused, which, in turn, decreases the residence time and increases the speed at which polymeric compositions can be processed into an end product, resulting in a faster, more efficient and economical process.
Plasticizers are available in a wide variety of alternative chemistries and include: 1) general purpose, 2) specialty types and 3) secondary and diluent types, more fully described herein. Plasticizers are also distinguished based on their ability to solvate dispersed solid polymers and/or their gelation and fusion temperatures in plastisols. Gelation and fusion temperatures dictate the speed of production and are influenced by the solvating power of the plasticizer. By way of example only, the gelation and fusion temperatures of a plastisol containing a dibenzoate plasticizer will be lower than a plastisol containing a general purpose phthalate, thus enabling speed of processing in that particular application.
General purpose plasticizers provide an excellent compromise between performance characteristics and economy for most applications. Some examples include: bis (2-ethylhexyl phthalate) (DEHP or DOP), diisononyl phthalate (DINP), dioctyl phthalate (DnOP), diisodecyl phthalate (DIDP), dipropylheptyl phthalate (DPHP), di-2-ethylhexyl terephthalate (DOTP or DEHT), and diisononyl-1,2 cyclohexane dicarboxylate (DIDC, an example of which is BASF's Hexamoll® DINCH®).
Environmental scrutiny has led to the development of “next generation” general purpose non-phthalate plasticizers, such as DOTP and DIDC. Even though DOTP, chemically, is a phthalate, it is not an orthophthalate, the use of which is subject to increasing regulatory pressure. These “next generation” phthalate alternatives are viable; however, they do not always give the performance desired in vinyl compositions, particularly in plastisols (i.e., they have poorer compatibility, slow speed, high gel temperatures, low gel strength). Blends of plasticizers can be used to adjust performance, although there may be some limits to this approach.
Some applications, however, require performance that cannot be achieved by use of a general purpose plasticizer alone. Applications that require better resistance to oils and solvents are one such example. General purpose phthalates are easily extracted by nonpolar solvents such as hexanes, such that alternative plasticizers would be a much better choice. There is also a need for plasticizers that are higher solvators for PVC and other polymer applications. These high solvators should also have a favorable rheology profile.
Specialty type plasticizers were developed, in part, to fulfill the need for high solvators, the most popular being lower molecular weight phthalates. An example of such a plasticizer is butyl benzyl phthalate (BBP), which is often employed as a high solvating plasticizer. Di-n-butyl phthalate (DBP) and diisobutyl phthalate (DIBP) are also useful high solvator, specialty type plasticizers. Examples of non-phthalate, high solvating plasticizers include dibenzoate esters, some citric acid esters, alkyl sulfonic acid esters, and certain phosphates. Dibutyl terephthalate (DBTP) and N-alkyl pyrrolidones have also been proposed as specialty type, high solvator plasticizers. Most high solvating plasticizers are limited in their usefulness due to high viscosity or poor rheology characteristics when incorporated into a plastisol. An ideal plasticizer possesses a good balance between solvation and rheology characteristics.
Benzoate plasticizers include dibenzoates and monobenzoates, such as diethylene glycol dibenzoate (DEGDB) and dipropylene glycol dibenzoate (DPGDB) esters that have been used in a wide variety of polymer applications, including in the vinyl industry. DEGDB is an excellent plasticizer, but due to its high freeze point, blends with DPGDB were also developed to capitalize on the utility and lower cost of DEGDB. Several years ago a blend of DEGDB, DPGDB and triethylene glycol dibenzoate (TEGDB) was introduced as a high solvating dibenzoate blend. More recently, a new dibenzoate triblend was introduced as a low VOC plasticizer/coalescent for use in plastisols, adhesives, architectural paint and coatings, and polishes, among other applications. This triblend, comprising DEGDB, DPGDB and 1,2-propylene glycol dibenzoate (PGDB) in various ratios and sold as K-FLEX® 975P, has been found to be very versatile for a variety of applications, based on its broad range of compatibilities with polymers utilized in the coatings industry (for example, in vinyl acrylic, acrylic and styrene acrylic types) and possesses good solvating properties and low volatility. Its performance properties compare favorably to traditional high solvating phthalate plasticizers as well as traditional benzoate ester plasticizers. Results set forth herein show the triblend to be a high solvating plasticizer that enhances the performance properties of 1,2-cyclohexane dicarboxylate esters, such as 1,2-cyclohexane dicarboxylic acid diisononyl ester, commercially available through a number of manufacturers, one example of which is BASF's Hexamoll® DINCH®.
Monobenzoate esters known to be useful as plasticizers include: isodecyl benzoate, isononyl benzoate, and 2-ethylhexyl benzoate. For example, isodecyl benzoate has been described as a useful coalescent for paint compositions and for use in the preparation of plastisols in U.S. Pat. No. 5,236,987 to Arendt. The use of isodecyl benzoate has also been described in U.S. Pat. No. 7,629,413 to Godwin et al. as a useful secondary plasticizer in combination with phthalate plasticizers to provide lower viscosity and lower volatility in PVC plastisols. The use of 2-ethylhexyl benzoate in a blend with DEGDB and diethylene glycol monobenzoate is described in U.S. Pat. No. 6,689,830 to Arendt et al. The use of isononyl esters of benzoic acid as film-forming agents in compositions such as emulsion paints, mortars, plasters, adhesives, and varnishes is described in U.S. Pat. No. 7,638,568 to Grass et al.
“Half ester” monobenzoates include dipropylene glycol monobenzoate and diethylene glycol monobenzoate, which are byproducts of the production of dibenzoates, but which, most of the time, are not objects of production. Half esters are not known for being high solvators, although they may be used in conjunction therewith. Half esters are also not as useful as dibenzoate plasticizers, because they are less compatible than the corresponding dibenzoate with PVC. However, the half esters are compatible with emulsion polymers, such as acrylic and/or vinyl ester polymers.
Examples of secondary and diluent type plasticizers, used primarily to reduce plastisol viscosity, include those based on castor oil and soybean oil. Isodecyl benzoate, a monobenzoate, is also a useful diluent type plasticizer.
All of the high solvator plasticizers (regardless of type) add value to vinyl compositions that traditional general purpose plasticizers cannot. Traditional general purpose plasticizers have good rheology profiles and are compatible with many polymers, but have poor solvating ability. Moreover, many of the high solvator plasticizers are phthalates, for which safer alternatives are being sought.
There remains a need for non-phthalate, low VOC plasticizers for use in polymeric applications, such as plastisols, as alternatives to traditional diluent plasticizers. These alternatives should be compatible with a wide variety of polymers and have lower VOC content and comparable or better performance properties, when used in polymer applications, such as vinyl, traditionally requiring plasticizers. Non-phthalate, low VOC alternatives are particularly desirable in view of environmental, health and safety issues associated with many of the traditional diluent type plasticizers.
It has been discovered that an entirely different monobenzoate, 3-phenyl propyl benzoate (3-PPB), is a surprisingly effective plasticizer alternative for use in polymeric applications, including but not limited to plastisols, paints and other coatings, adhesives, OPV's and inks. Besides lower VOC's, advantages of this monobenzoate, versus conventional higher VOC diluent plasticizers, such as 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, are its excellent health, safety and environmental profile and handling properties, which are better than most dibenzoates and monobenzoates previously used.
The inventive monobenzoate, 3-PPB, has been found to be an excellent blending plasticizer in combination with traditional plasticizers, such as dibenzoates, phthalates, 1,2-cyclohexane dicarboxylate esters, and the like, resulting in plastisols that are lower in viscosity, but having better gel/fusion characteristics than that obtained with blends of traditional plasticizers. In particular, the inventive monobenzoate achieves excellent performance benefits when used alone in a blend with diisononyl-1,2-cyclohexane dicarboxylate or other general purpose plasticizers such as DOTP and DINP. It also achieves excellent performance benefits when combined with a unique dibenzoate triblend and diisononyl-1,2-cyclohexane dicarboxylate. In addition, results achieved show that the unique triblend of dibenzoates alone, without the inventive monobenzoate, also achieves excellent performance benefits when blended with diisononyl-1,2-cyclohexane dicarboxylate.
The monobenzoate, 3-PPB, has been used in the past in flavoring and fragrance applications, but not in polymeric applications of the type discussed herein. It continues to be used in flavoring and fragrance applications. It has also been used as a solubilizer for certain active or functional organic compounds in personal care products, such as topical sunscreens, as described in U.S. Patent Publication 2005/0152858.
While this invention is focused on the use of the inventive plasticizer and/or blends thereof in plastisol compositions, other applications include use in a variety of coatings, including without limitation overprint varnishes, polishes, inks, paints, adhesives, sealants, and caulk, which are the subject of co-pending applications.
It is an object of the invention to provide a plasticizer having excellent compatibility with a wide variety of polymers and lower VOC content than traditional diluent type plasticizers used to control plastisol viscosities, for use alone or in blends with other plasticizers, in plastisols and other polymeric applications where plasticizers are traditionally required.
It is a further object of the invention to provide a non-phthalate alternative plasticizer for use as a primary or secondary plasticizer in PVC applications.
It is another object of the invention to provide a non-phthalate plasticizer or plasticizer blend that has high solvating properties and a good rheology profile, which is useful to improve the compatibility and processability of poor solvating plasticizers, while minimizing the attendant disadvantages of high viscosity and poor rheology associated with the use of high solvating plasticizers.
Still a further object of the invention is to provide plasticizer blends comprising the inventive monobenzoate of the invention with general purpose and other plasticizers, including but not limited to a blend of the inventive monobenzoate alone with DOTP, DINP, diisononyl-1,2-cyclohexane dicarboxylate, a unique dibenzoate triblend, or mixtures thereof.
Yet another object of the invention is to provide a plastisol formulation utilizing a non-phthalate plasticizer, 3-PPB, which allows faster processing and economic efficiencies to be achieved and provides comparable or better tensile strength properties over traditional diluent type plasticizers.
Other objects of the invention will be apparent from the description herein.